Method of purifying sewage and recovering organic matter therefrom.



. e. w. Mugs. METHOD OF PURIFYING SEWAGE AND RECOVERING ORGANIC MATTERTHEREFROM. APPLICATION FILED FEB-15, 1914.

31. 1 34,?8Qh Patented Apr. 6, 1915.

p I a ms RWY OR 'is adapted to such nnirnn snares raarnn'r orationGEORGE WELLINGTON MILES, OF BELMONT, MASSACHUSETTS, ASSIGNOR T0HHIISELF,

TRUSTEE.

Specification of Letters Patent.

Patented Apr. 6, 1915,

Application filed February 16, 1914. Serial No. 818,854.

To all whom it may concern Be it known that I, GEORGE WELLINGTON MILES,a citizen of the United States, and resident of Belmont, in the countyof MiddleseX and State of Massachusetts, have invented new and usefulImprovements in Methods of Purifying Sewage and Recovering OrganicMatter Therefrom, of which the following is a specification.

My invention relates to the purification of sewage, and is addressedparticularly to the treatment of sewage in large quantities, such as aredelivered by modern city mains.

The object of my invention is the precipitation, deposit, retention andeconomical disposition of bacterial, organic, and other recoverableconstituents of city sewage, so that the effluent water thereof may bedischarged into streams or harbors without polluting them, or at allevents, without sensibly increasing the normal and natural bacterialcontent of such waters. The chief difficulty presented is the enormousvolume of sewage daily discharged from city mains, the relatively smallpercentage of the organic and bacterial contents of such sewage, and theparamount necessity for substantially continuous discharge of sewage,which must be moved to make place for the constantly accumulating sewagefrom the myriad source in a city.

A further object of my invention is the destruction of the comparativelytrifling content of bacteria left as a residue in the efliuent after thephysical separation therefrom of the major portion of bacteria with theorganic matter previously in suspension. Whether or not the completeelimination of bacteria from the sewage-effluent shall be accomplishedby my method or by my methodin that specific aspect thereof whichcomplete elimination, will depend on the conditions to be met, or thepreferences of those who employ the method.

Sewage from city mains contains organic and putrescible matter insolution, or it may be in colloidal suspension, in the slightly alkalinewater-vehicle. This organic matter is so attenuated that the sewageitself 'is usually no more turbid or clouded than some pondwater orsurface water. matter has associated with it miscellaneous bacterialorganisms, in such quantity that This organic the modern practice ofdischarge sewage into streams or harbors involves a serious degree ofpollution of such waters.

To clarify and render substantially bacteria-free the sewage effluent mymethod is applied to precipitate and fiocculate the attenuated,suspended, dissolved and diffused organic matter and to allow the sameto settle and deposit itself at the bottom of suitable settling basinssuch as are already provided in many places, as for instance the MoonIsland sewage reservoirs of the system of Boston, Massachusetts; thenthe purified effluent, physically separated from the organic matter andbacteria associated therewith may be discharged into streams or harborsharmlessly.

In general my method consists in introducing into the moving streamofsewage in a city main, an inorganic acid, preferably sulfuric acid, ata rate predetermined by a series of tests, then thoroughly distributingthe inorganic acid through the liquid body of sewage as the sameproceeds through the main, while avoiding any material obstruction tothe general flow, thereafter allowing the acidified sewage to stand insettling basins of adequate volume for such time as is required to allowthe acid to have the effect hereinafter described. The rate at which theacid is supplied to the moving sewage should be such as will give thesewage as a whole after the action of the acid is completed, a slightlyacid reaction. The inorganic acid destroys the agent which holds theorganic suspension; probably this subdivision and suspension is due tothe presence of alkaline protective colloids, the removal or destructionof which leaves the organic matter free to flocculate, coagulate. andthen settle to the bottom of the sewage. Such alkaline protectivecolloids are amply accounted for by the invariable presence in citysewage of alkaline soaps and greases. When a quantity of inorganic acidsufficient to produce an acid reaction in the sewage has been addedthereto, the acid reaction evidences the fact that enough acid has beensupplied to perform the work of rendering the organic matter free toflocculate, and thereafter settle. As the bacteria in sewage areintimately associated with the organic matter therein, the sedimentationof the organic matter in subdivision and matter segregates the bacterialalso, leaving no conducted as to either liquid or gaseous,

the liquid vehicle substantially free from bacteria. By substantiallyfree, I mean that the bacterial content is so far reduced that it is notlarger than that frequently found in acceptable drinking vwater; saywell within one thousand to the cubic centimeter. 7

In the drawings hereto annexed, Figure 1 is a diagram illustrating inplan an apparatus by which my invention may be carried into effect; andFig. 2 is a diagram in section at 2-2 of Fig. 1.

In these diagrams, which represent part of a sewage main, M and M aresections of the main, and M another section thereof to which an acidsupply pipe A, with delievery ends a, a, is led.

P represents a source from which acid, is pumped into the pipe A. Themain section M is made sinuous so that the sewage will swirl about afterleaving the section M, and stirred on its way to either of the settlingbasins B. In practice, at least two such basins will be pro; vided withsuitable means, such as gates G and branches M for delivering the sewageinto the basins alternately; an acidifying apparatus such as indicatedwill be installed in the sewer main leading to said branches, so thatthe sewage delivered .to either basin shall be charged with acid. Bysuch means as this above described, the whole body of sewage will beuniformly acidified and the acid, when the sewage comes to rest in thesettling basin, will be uniformly distributed. The final sedimentationof organic matter will be complete in from six or more hours after thesewage, with inorganic acid distributed therethrough, has stood in thesettling basin. The discharge of purified effluentmay then take place,and should be so avoid disturbing and redistributing the depositedprecipitate, al-

. though the escape of a portion of it with the efliuent will do farless harm than the sewage as originally constituted, since theprecipitate will settle out of the eflluent and be quite limited indistribution.

If it be desired to purify the sewage still more completely than will bethe case when the above described mode is employed, I introduce into thesewage or cause to be formed erein, an inorganic acid which by reactionwith the bases contained in the sewage will form acid salts, which inthemselves constitute effective bactericidal agents. For example, mypreferred mode of accomplishing this result is to iniect into the sewagea quan-' tity of sulfur dioxid (S0,) suflicient to neutralize the normalalkalinity of the sewage and give it an acid reaction. The sulfur dioxidproduces sulfurous acid (H which like the sulfuric acid employed in themode first above described, alters the conditions which are productiveof or favorable to distribution and suspension of organic matter, andalso, by reaction on the bases present, produces acid salts, such assulfites, which in solution'in the sewage destroy the bacteria remainingin the purified efiluent after the sedimentation of organic matter. Bythis specific method the sewage efiluent can be made absolutelybacteria-free.

Whether the purifying acid be liquid or gaseous, it is to be introducedinto the sewage while it is in flow through the main, so that thesubsequent movement of the sewage stream may be availed of as the meansfor thorough distribution of the acid in the liquid mass which is sovoluminous in the case of city sewage, and so attenuated, that completeadmixture of acid cannot prac- V tically be effected by mechanicalstirring after the sewage is collected in the settling basin. By thismode of acidifying the sew.- age in transit the utmost economy of acidcan be obtained. Mechanical stirrers may be employed, if desired, toeifect a thorough distribution of acid through the sewage.

The sedimentation of organic matter may be effected in extensions of themains, provided these are long enough, and the flow gentle enough toallow the deposit of organic matter. Settling basins, are however, to bepreferred.

The organic and bacterial matter in suspension in normal city sewage isso microscopic, so attenuated in its distribution, and so constituted asto its individual particles, as to be non-precipitant for all practicalpurposes. If protected from all agencies provocative of precipitation(sunlight and air, for instance) this organic matter is probably totallyand persistently non-precipitant. action of the inorganic acid (abovedescribed) is to render precipitant this normally non-precipitantorganic matter. which thereupon flocculates and precipitates from thewater vehicle in a relatively short time. Since. as above stated, theinorganic acid is introduced into the sewage as it flows in the main, ithas its effect on the finely divided organic matter before the latterhas undergone any material degree of natural decomposition orputrefaction. Emerging from the main, normal city sewage is notoffensive to any marked degree, showing that decomposition of organicmatter has, to all practical intents, not set in. Decomposition, whichinevitably ensues after the organic matter has been exposed for a time,destroys the organic matter as such, producing more or less ofiensivegases and an inorganic residue which is analogous to ash. It would beinconsistent with the economic values of the within described process aswell as with its sanitary and aesthetic objects, to allow sewage toputrefy to any marked. degree before rendering'the organic matterprecipitant in The preliminaryor preparatory nisaaeo the mannerdescribed and thus conditioning it for prompt removal and recovery,because decomposition destroys the organic matter and the recoverablevalues in proportion to its progress, while generating ofiensive gases.

The organic matter in sewage has heretofore been precipitated by theaddition of soluble metallic salts, such as alum or ferric sulfate, andthe effluent clarified. It has also been proposed to employ an inorganicacid, such as sulfuric acid, in conjunction with such metallic salts.The presence of soluble metallic salts, either with or without aninorganic acid, while effective to cause precipitation and sedimentationof organic matter, nevertheless precipitates such matter in a conditionwhich resists economical recovery of the grease-values, for the reasonthat the metallic salts, reacting on the fatty acids present in theorganic matter, form insoluble soaps. These insoluble soaps increase thedifliculty and expense of recovery of grease values and thus defeat anyeconomic object, leaving only the sanitary and aesthetic purposes ofsewage treatment fulfilled. My process, as distinguished from theseearlier methods, is characterized by the employment of an inorganic acidas the sole efiective reagent to render the organic matter precipitable,and by conditions which preclude the detrimental formation of insolublesoaps.

What I claim and desire to secure by Letters Patent is:

1. The method of purifying sewage and recovering therefrom normallynon-precipitant organic matter, which consists in introducing into thesewage before decomposition of the said organic matter has materiallyprogressed, an inorganic acid as the sole efiective reagent, to rendersaid organic matter precipitant, allowing the said organic matter, afterit has become precipitant by the agency of the acid, to precipitate, andsubsequently separating the cleared liquid from the precipitate.

2. The method of purifying sewage and recovering therefrom normallynon-precipitant organic matter, which consists in introducing into thesewage, before decomposition of the said organic matter has materiallyprogressed, an inorganic acid under conditions which preclude theformation of insoluble soaps, to render said organicmatterprecipitantfallowing the said organic matter, after it has becomeprecipitant by the agency of said acid, to precipitate, and

subsequently separating the cleared liquid from the precipitate.

3. The method of purifying sewage and recovering therefrom normallynon-precipitant organic matter, which consists in in troducing sulfurousacid into the sewage before decomposition of the said organic matter hasmaterially progressed, thereby rendering precipitant the said organicmatter, and subsequently separating the cleared liquid from theprecipitate.

a The method of purifying sewage and recovering therefrom normallynon-precipitant organic matter, which consists in introducingsulfurdioxid into the sewage before decomposition of the said organicmatter has materially progressed, thereby producing sulfurous acid,rendering precipitant the said organic matter, and subsequentlyseparating the cleared liquid from the precipitate.

Signed by me at Boston, Massachusetts, this ninth (.9) day of February1914.

GEORGE WELLINGTUN MILES.

Witnesses:

ODIN RoBER'rs, G. WRIGHT ARNOLD.

